1. Field of the Invention
The present invention relates to a magnetic recording medium and a method of smoothing a surface of the magnetic recording medium.
2. Background Arts
A magnetic tape is widely used as a magnetic recording medium for recording audio signals and/or video signals. To manufacture the magnetic tape, a surface of a long web of non-magnetic base film is coated with a magnetic layer that is made by dispersing a magnetic material and a binder material in a solvent, wherein the binder material is composed of a resin and a curing agent. Thereafter, the magnetic layer is subjected to treatments for orienting the magnetic fields and the like. After drying the magnetic layer, the long web coated with the magnetic layer is slit into a predetermined width, and is coiled into a roll.
Because the magnetic tape manufactured in this way has many granular components, like insufficiently-fixed ferromagnetic powers, on the surface of the magnetic layer. These insufficiently-fixed granular components can drop off the magnetic tape as the tape is moved by a magnetic head, and stain the surface of the magnetic head, damaging the quality of the recorded or reproduced signal. As the ferromagnetic powers removes off the magnetic layer, the electromagnetic conversion characteristics of the magnetic recording medium deteriorates, which appears as an output power reduction.
To avoid this problem, a process of smoothing the surface of the magnetic layer is carried out prior to slitting the magnetic tape. In the smoothing process, the surface of the magnetic layer is abraded by means of an abrasive tape, and then ground by means of a grinding tool that is made of a very hard material, like artificial sapphire or ruby, or carbide alloy, thereby to remove the insufficiently-fixed granular components or extraneous substances deposited on the magnetic layer. Thereafter, because shavings produced by the abrading and grinding of the magnetic layer may be deposited on the surface of the magnetic layer, the magnetic tape is subjected to a cleaning process for cleaning the shavings off the magnetic layer.
The grinding tool used in the smoothing process for the magnetic layer has conventionally been fixed in position, so the contact position of the grinding tool with the magnetic layer is maintained unchanged. As a result, the grinding tool is worn off earlier around the contact position, which results a stepped portion on the edge of the grinding tool. The stepped portion provides scratches or scuff marks on the magnetic layer.
In view of the foregoing, an object of the present invention is to provide a magnetic recording medium free from scuff marks and scratches on its surface.
Another object of the present invention is to provide a method of smoothing a surface of a magnetic recording medium.
In a magnetic recording medium manufactured by coating a long web of non-magnetic base material with a magnetic layer, according to the present invention, a surface of the magnetic layer of the magnetic recording medium is ground by at least a grinding tool that is moved back and forth in a transverse direction to the long web, while the magnetic recording medium is being conveyed in a lengthwise direction of the long web.
Since the grinding tool is moved back and forth in the transverse direction, the grinding tool would not be kept contact in the same portion with the magnetic recording medium, but the portion of the grinding tool that is in contact with the magnetic recording medium and is thus grinding the surface of the magnetic layer changes continually. Accordingly, the problem of partial abrasive wear of the grinding tool would not arise, so the grinding tool is prevented from having a stepped portion on its edge. Thus, the magnetic recording medium of the present invention is free from the scuff marks or the scratches that could otherwise be caused by the stepped portion.
According to another aspect of the present invention, a method of smoothing a surface of a magnetic layer of a magnetic recording medium after manufacturing the magnetic recording medium by coating a long web of non-magnetic base material with the magnetic layer, comprising the steps of putting at least a grinding tool on the surface of the magnetic layer with an edge of the grinding tool oriented in a transverse direction to the long web; and moving the grinding tool back and forth in the transverse direction while conveying the magnetic recording medium in a lengthwise direction of the long web.
According to a preferred embodiment, a plurality of the grinding tools are arranged at regular intervals along the conveying direction of the magnetic recording medium, and adjacent two of the grinding tools are moved in opposite directions to each other. Thereby, the magnetic recording medium is prevented from fluctuating in the widthwise direction during the grinding.
It is preferable to move the grinding tool at a high speed in initial and final stages of one stroke, and at a low speed in a middle stage of one stroke. This configuration enforces the effect of preventing the partial abrasive wear of the edge of the grinding tool.